What are the characteristics of bacteria?
- no true nucleus (prokaryotes)
- may have plasmids that provide extra functions (eg. antibiotics resistance)
- most with a single chromosome
- have cell wall (except mycoplasma)
- with different shapes
=> sphere: coccus
=> rod-shaped: bacillus
=> spiral: spirochete or spirillum
What are the forms of cocci bacteria?
- diplococcus (in pairs)
- tetracoccus (in groups of 4)
- streptococcus (in chains)
- staphylococcus (in grape-like clusters)
What are the structures of a bacterial cell?
- pili –> enable bacteria to adhere to surfaces
- flagella –> enable motility
- capsule –> inhibit phagocytosis
- cell wall –> provides rigidity, strength and protection
- plasma membrane
- ribosome –> site of protein synthesis
- nucleoid region (DNA)
What are the functions of bacterial cell wall? What is the rigid part of the cell wall made of? What is the use of Gram staining?
- to provide rigidity and protect cell shape & against osmotic damage
- made up of peptidoglycan
- to distinguish bacteria with different cell wall composition –> Gram +ve (purple); Gram -ve (pink)
What is the difference between Gram +ve and -ve bacteria?
- Gram +ve
=> thick peptidoglycan cell wall –> retain crystal violet after washing by alcohol –> purple - Gram -ve
=> thin peptidoglycan cell wall (lipoprotein and protein in outer membrane) –> crystal violet easily washed away by alcohol –> counterstained by safranin –> pink
How to perform Gram staining?
- first stage: smear preparation
=> smear bacterial sample on the slide and left to air dry
=> heat fixing the smear briefly by passing the slide through the Bunsen burning - second stage: staining
=> staining with crystal violet
=> add iodine to stabilise crystal violet staining
=> decolourization by alcohol –> gram -ve bacteria becomes colourless
=> counterstaining with safranin. Gram +ve will remain purple and Gram -ve are stained pink
What are the three external structures in bacteria and their respective functions?
- capsule
=> layers of anti-phagocytic polysaccharides or protein that surround the cell wall - flagella
=> long, rope-like structures for movement - pili
=> short, hair-like appendages anchored in plasma membrane
=> somatic pili –> for attachment to host cells
=> sex pili –> for transfer of plasmid DNA from bacterium to another
What are the characteristics of endospores? How are they formed and worked? What special thing about endospores? How are the spored killed? How do sterilisation procedures relate to endospores?
- resistant to heat, desiccation, ultraviolet light and chemicals
- formed inside the original cell –> remain dormant for years –> form new cells when conditions are favourable
- most notorious bacteria are spore-formers
- killed by autoclaving (>120 degree Celsius at elevated pressure)
- sterilisation procedures are assessed by their ability to inactivate endospores
What are the steps of bacterial reproduction? How do they reproduce? What is the doubling time? What is the example?
- cell elongation –> DNA replication –> cross wall completed –> daughter cells separate
- reproduce by binary fission
- 15-30 minutes
- a single E. coli cell in a nutritionally complete medium –> >10 million in just 8 hours
What are the stages of the bacterial growth curve?
- lag phase: growth and reproduction just begin
- log phase: exponential growth phase
- stationary phase: cell growth=cell growth due to limited environmental factors (eg. nutrients)
- death phase: cell death > cell growth (eg. toxic wastes accumulate)
What are the types of bacteria with different oxygen requirement?
- obligate aerobes: grow only with the presence of oxygen
- anaerobes: able to grow in the absence of oxygen
=> obligate: killed by O2 (eg. bacteria in gut)
=> aerotolerant: unaffected by O2
=> facultative: grow in both anaerobic and aerobic conditions but grow best with O2
=> microaerophiles: grow at low [O2] but killed by high [O2]
What are the characteristics of pathogenic bacteria? What are the types of toxins?
- flagella: escape from phagocytes
- capsule: anti-phagocytic
- pili: for attachment to host surfaces
- toxins
=> endotoxins: released by dead Gram -ve bacteria (cell wall) –> fever and septic shock
=> exotoxins: toxic protein released by living bacteria (usually Gram +ve)
=> neurotoxins: cause damage to the brain
=> enterotoxins: cause intestinal diseases
What are the general features of Staphylococcus aureus?
- Gram +ve cocci (round; grape-like clusters)
- facultative anaerobes
- catalase and coagulase +ve
- non-motile
- normal flora of skin but may cause opportunistic infections which are difficult to treat
- transmitted by person-to-person contact, blood and ingestion of enterotoxins
What are the diseases caused by Staphylococcus aureus?
- major cause of nosocomial infections
- most disease are caused by the presence of toxins in:
=> blood: toxic shock syndrome (TSS) toxins –> TSS –> fever, chill, diarrhoea and vomiting –> shock –> coma
=> intestine: heat-resistant enterotoxins –> food poisoning –> diarrhoea and vomiting
=> skin –> inflammation and skin lesions
What is the treatment of S. aureus? What may be the risk result?
- requires aggressive treatment by antibiotics (methicillin)
- excessive use of methicillin –> methicillin-resistant S. aureus (MRSA) –> serious nosocomial infections (surgical wounds) –> bacteremia –> high mortality
How to prevent S. aureus? What is the reason for the present treatment? What is the alternative treatment for MRSA?
- wash hands before and after contact with food or infected individuals
- use of methicillin –> resistant to penicillin because they produce an enzyme (beta-lactamase) that digest penicillin
- treated with alternative antibiotics (vancomycin)
What are the general features of Streptococcus pneumoniae?
- Gram +ve cocci (round, in chains or pairs)
- facultative anaerobes
- catalase -ve
- non-motile
- normally present in the throat and nasopharynx
What diseases can be caused by Streptococcus pneumoniae?
- pneumonia
=> inflammation of the lungs –> fever, shortness of breath, chill and cough –> death in old adults, especially cancer patients with weak immunity - meningitis
=> inflammation of the protective membrane covering the brain and the spinal cord –> high mortality
How is S. pneumoniae spread? What is the treatment and prevention?
- spread through droplets (coughing and sneezing)
- treated by antibiotics (eg. penicillin for pneumonia and vancomycin for resistant strains)
- prevented by good hygiene
=> wash hands
=> cover mouth and nose when coughing/ sneezing
=> vaccination
What are the general features of Escherichia coli?
- Gram -ve bacilli (rod-shaped)
- facultative anaerobes
- catalase +ve but oxidase -ve
- motile (presence of antigen H)
- have 3 types of antigens (O,K,H)
- normal flora of colon but can cause disease when they get genes from other organisms –> pathogenic E. coli –> invasion and production of toxins
- can be found in decal-contaminated food or water
What are the diseases caused by E. coli?
- diarrhoea (gastroenteritis)
=> due to heat-labile enterotoxin produced by enterotoxigenic E. coli –> hypersecretion of Cl- and inhibition of Na+ reabsorption in gut –> watery faces - urinary tract infections (UTI)
=> common cause of bladder and kidney infections - bloody diarrhoea and hemolytic-uremic syndrome (HUS)
=> caused by enterohemorrhagic E. coli (O157:H7) –> destruction of villi and RBCS –> blood diarrhoea and renal failure
What are the source and symptoms of Enterohemorrhagic E. coli?
- cattle/ cow that are infected –> uncooked meat or unsterilised milk
- fruit or vegetables contaminated by the faces of infected animals
- fever, diarrhoea, vomiting, stomach muscle spasm
What are the preventions and treatment of E. coli infection?
- good hygiene and clean food
- thoroughly cook ground beef and pasteurise milk
- carefully wash and thoroughly cook vegetables before consumption
- diarrhoea can be treated by intake of fluid and electrolytes; extraintestinal diseases need antibiotics
